The present invention relates to a scroll fluid machine such as a scroll compressor, a scroll vacuum pump, a scroll expander or a scroll blower.
Such a scroll fluid machine comprises an orbiting scroll supported on an eccentric shaft portion of a drive shaft to turn, and a stationary wrap comprising a stationary end plate having a stationary wrap. An orbiting wrap on an orbiting end plate of the orbiting scroll engages with the stationary wrap to form a sealed chamber between the stationary and orbiting wraps. The scroll fluid machine has a self-rotation preventing device for preventing the orbiting scroll from rotating on its own axis.
By the eccentric shaft portion of the drive shaft and the self-rotation preventing device, the orbiting scroll is eccentrically revolved so that the volume in the sealed chamber gradually decreases toward the center for compression or increases away from the center for depressurizing to discharge from the outer circumference.
The ends of the orbiting and stationary wraps have engagement grooves in which tip seals fit in sliding contact with the opposing end plates sealingly.
In the scroll fluid machine, U.S. Pat. No. 6,695,597 discloses a dust seal on the outer circumference of engagement area of orbiting and stationary wraps. The dust seal comprises a circle; a partially-separated circle the ends of which are contacted or made close; a partially-separated circle the ends of which are engaged with an outer side face of an outermost tip seal; the same as part of a tip seal; and a seal member on the outermost wrap contacting the other sliding surface, as known from the US Patent and other references.
However there are disadvantages in the dust seal of the known scroll fluid machine as below.
(a) circle
The circular dust seal fitted in an annular groove requires quite high accuracy in size and a lot of works and technique. Furthermore, heat and sideward pressure generated with operation stretches or the annular groove is deformed to cause unsuitable fitting. Deviation of the dust seal in the annular groove causes failure in sealing.
(b) partially separated circle the ends of which contacts or become close
To absorb thermal expansion of the dust seal, a little gap has to be formed between the ends in advance. But it is impossible to prevent dust from coming in through the gap completely. To prevent this, the ends of the dust seal are tilted or overlapped, but such working is troublesome to increase cost. The dust seal is likely to move in the annular groove circumferentially.
(c) partially separated circle the ends of which contacts the outer side surface of the outermost tip seal
The annular groove must be formed noncircular, which is not so easy for working. During operation, a gap is formed between the end of the dust seal and the outer side surface of the tip seal, so that dust is introduced through the gap.
(d) partially the same as the tip seal
The annular groove must communicate with an engagement groove for the tip seal, which requires a lot of work and technique to increase cost. The dust seal is integrally formed with the tip seal or the end is partially contacted with the outer side surface of the tip seal, which causes the disadvantages as above.
(e) A seal member of the outermost wrap on the opposite sliding surface
A groove in which the seal member engages becomes complicate in shape to make working troublesome and increase cost. The tip seal wears to cause failure in dust sealing.